/* Receiver/client multicast Datagram example. */
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct sockaddr_in localSock;
struct ip_mreq group;
int sd;
int datalen;
char databuf[1024];

int main(int argc, char *argv[])
{
    if (argc < 4) {
        printf("Usage: %s groupAddr port localIfAddr\n", argv[0]);
        return 0;
    }
    char *grpAddr = argv[1];
    int  port = atoi(argv[2]);
    char *localIfAddr = argv[3]; 

    /* Create a datagram socket on which to receive. */
    sd = socket(AF_INET, SOCK_DGRAM, 0);
    if(sd < 0)
    {
        perror("Opening datagram socket error");
        exit(1);
    }
    else
        printf("Opening datagram socket....OK.\n");

    /* Enable SO_REUSEADDR to allow multiple instances of this */
    /* application to receive copies of the multicast datagrams. */
    {
        int reuse = 1;
        if(setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof(reuse)) < 0)
        {
            perror("Setting SO_REUSEADDR error");
            close(sd);
            exit(1);
        }
        else
            printf("Setting SO_REUSEADDR...OK.\n");
    }

    /* Bind to the proper port number with the IP address */
    /* specified as INADDR_ANY. */
    memset((char *) &localSock, 0, sizeof(localSock));
    localSock.sin_family = AF_INET;
    localSock.sin_port = htons(port);
    localSock.sin_addr.s_addr = INADDR_ANY;
    if(bind(sd, (struct sockaddr*)&localSock, sizeof(localSock)))
    {
        perror("Binding datagram socket error");
        close(sd);
        exit(1);
    }
    else
        printf("Binding datagram socket...OK.\n");

    /* Join the multicast group 226.1.1.1 on the local 203.106.93.94 */
    /* interface. Note that this IP_ADD_MEMBERSHIP option must be */
    /* called for each local interface over which the multicast */
    /* datagrams are to be received. */
    group.imr_multiaddr.s_addr = inet_addr(grpAddr);
    group.imr_interface.s_addr = inet_addr(localIfAddr);
    if(setsockopt(sd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&group, sizeof(group)) < 0)
    {
        perror("Adding multicast group error");
        close(sd);
        exit(1);
    }
    else
        printf("Adding multicast group...OK.\n");

    /* Read from the socket. */
    datalen = sizeof(databuf);
    if(read(sd, databuf, datalen) < 0)
    {
        perror("Reading datagram message error");
        close(sd);
        exit(1);
    }
    else
    {
        printf("Reading datagram message...OK.\n");
        printf("The message from multicast server is: \"%s\"\n", databuf);
    }
    return 0;
}

